The technical field to which the invention relates is a gas turbine engine combustor with the flexibility of using liquid fuel or natural gas fuel nozzles interchangeably. Many combustors for industrial engines in the prior art include dual fuel nozzles that are mounted in combustor walls and can receive both liquid fuel and natural gas fuel at the same time for mixing with compressed air.
The invention however is most advantageously applied to an aero derivative industrial gas turbine engine. Such engines are used for stationary industrial applications but incorporate the standard components from aircraft gas turbine engine designs for efficiency and economy in manufacturing and maintenance. An important feature of an aero derivative industrial gas turbine engine is the flexibility of utilizing liquid fuel or natural gas fuel as desired. An important advantage as well is that fuel nozzles operating on natural gas can be fitted into the same combustor interface as a liquid fuel nozzle. However, liquid fuel nozzles, and especially swirl-type nozzles, are not suitable for use with natural gas because natural gas molecules are much smaller than particles of sprayed liquid fuel aerosol. As a result, gas molecules would be trapped in the swirl envelope created by a conventional liquid fuel nozzle. Also, the heat distribution around the nozzle may be different than for a liquid fuel, resulting in hot spots on the combustor. The difficulty is, however, that if a typical natural gas fuel nozzle is used, the combustor would require redesign of the combustor and other components relative to the engine's aero-engine equivalent.
In the prior art, a conventional dual fuel nozzle is often used so that operators can select between natural gas fuel and liquid fuel without changing nozzles. However, such nozzles are relative complex requiring multiple bores, multiple manifolds and complex fuel and air mixing jets. Since nozzles are often replaced and coke build-up requires frequent maintenance, there are advantages to use of simple interchangeable nozzles that can be manufactured at minimal cost. There is a need, however, for a simple gas fuel nozzle which may be used in an aero derivative engine with minimal change to other components of the engine. There is also a need for a gas fuel nozzle which is capable of delivering a fuel/air mixture which is as similar as possible to the liquid fuel nozzle for which the aero version of the gas turbine engine was originally designed.
It is an object of the invention to permit simple conversion of existing liquid fuel nozzles to natural gas fuel nozzles with minimal nozzle, combustor or other design changes.
Further objects of the invention will be apparent from review of the disclosure, drawings, and description of the invention below.